This invention relates to an improved technique for sealing between members of a hammer union and more particularly to an improved seal assembly that replaces the existing seal of a hammer union.
In the testing and production of hydrocarbon wells, specialized couplings are provided which incorporate seals to prevent leakage between the coupling components. One such coupling is known as a union and comprises a coarse male thread on one of the components which cooperates with coarse female threads on a collar to provide a quick connect/disconnect coupling.
A more specialized quick connect/disconnect coupling is known as a hammer union which comprises four components: a thread end having coarse male threads on the exterior, a seal on the inside of the thread end, a nut end having a smooth nose abutting the seal and a hammer nut having coarse female threads on the interior and ears on the exterior which may be struck with a hammer to cinch up the coupling. Because hammer unions have the capability of being quickly connected and disconnected, they are widely used in temporary installations or in equipment which is expected to be disassembled periodically.
Hammer unions have not been redesigned in many decades. The seal in a conventional hammer union is a large annular rubber seal that is basically rectangular in cross section. One of the coupling components provides a groove or rabbit receiving the annular rubber seal which is compressed between the coupling components when they are cinched up, thereby providing a seal. The rubber component is exposed to gases, fluids and abrasives flowing in the interior flow passage of the coupling. This conventional seal has withstood the test of time and has basically been unchanged for at least fifty years.
One of the situations where hammer unions are widely used is in equipment to test gas wells after they are initially completed or after recompletion from one zone to another. Typically, regulatory agencies require that gas wells be tested to provide a measure of gas deliverability and pressure using chokes of several different size. To enforce these regulations, regulatory agencies often will not allow a well to be produced into a sales line before testing. Test equipment typically comprises a trailer having an inlet end for connection to the well head, a separator for separating gas and liquid, an orifice meter for measuring the gas from the well and an outlet for connection to a flow line leading to a flare.
Many gas wells, particularly those completed at depth, do not produce commercial quantities of natural gas until they are fraced. It is a tribute to the research of major oil companies and major oil field service companies that modern frac techniques convert large numbers of conventionally completed uneconomic wells into economic ones. A typical current frac job injects a liquid or gel containing 500,000 or so pounds of sand or other proppant under pressure into a well to create, propagate and prop open a vertical fracture extending many hundreds of feet away from a well bore to provide a high permeability flow path from a relatively low permeability formation to the well bore.
One of the facts of life of fracturing a well with a large quantity of sand or other proppant is that not all of the proppant stays in the hydrocarbon zone when the well is produced. When production starts, some of the proppant returns to the well bore and is produced at the surface.
Hammer unions are also widely used on drilling rigs to make mud line connections, to make connections in cementing operations and to pump various liquids into a well bore during completion operations.
Disclosures of some interest relative to this invention are U.S. Pat. Nos. 2,726,104; 3,140,107; 3,848,905; 4,930,791 and U.S. Patent Publication H945.
In this invention, it is recognized that new gas wells, particularly those that have been fraced, produce high velocity streams of proppant laden gas and liquid. Because the proppants are sand or similar particles, they are quite abrasive. These high velocity abrasive well streams have the capability of cutting out the conventional seals used in many flow line connections, specifically hammer unions. This creates a dangerous and awkward situation where highly flammable well production, both liquid and gas, escapes from a flow line at a location where it is unexpected. Instead of the well contents being flared at a flare installation hundreds of feet from the well head or test rig, all of a sudden, well contents are escaping in the test rig, immediately adjacent the well head or some other equally unsuitable location. Well testers and others in the immediate area have to be vigilant to detect the onset of large leaks in flow lines and test equipment and be prepared to shut the well in. It is a scary thing to shut in a well producing a high velocity stream loaded with proppant because of the danger of cutting out valves on the well head, leaving the well uncontrollable.
In this invention, flow line coupling seals, such as in hammer unions, are modified to provide a seal largely protected against the abrasive action of high velocity well contents. Specifically, the conventional all-rubber seal is removed and discarded. It is replaced by an annular metal insert or carrier having a small annular groove or rabbit receiving an O-ring or other much smaller seal. In this fashion, a seal protected against the action of abrasive high velocity well fluids is placed in the same groove as a conventional seal, meaning that the metal components of a conventional flow line coupling, such as a hammer union, do not have to be machined or otherwise modified to accommodate a seal providing a much longer useful life.
It is an object of this invention to provide an improved method and apparatus sealing a flow line coupling.
Another object of this invention is to provide an improved hammer union.
A further object of this invention is to provide a technique for changing the seal of a flow line coupling without machining or otherwise modifying the permanent metal components of the coupling.
These and other objects and advantages of this invention will become more apparent as this description proceeds, reference being made to the accompanying drawings and appended claims.